Radiation therapy systems can be used to provide treatment to patients suffering a variety of conditions. Radiation therapy can be used to perform selective cell destruction, useful in controlling cancers by treating tumorous tissue. An external source produces a collimated beam of radiation that is directed into the patient to the target site. A quantity of radiation can be directed into targeted tissue with the goal of damaging the targeted tissue while limiting or minimizing damage to non-targeted tissue.
The dose and placement of the dose must be accurately controlled to ensure that the tumor receives sufficient radiation and that damage to the surrounding healthy tissue is minimized. Radiation dosimetry is used to calculate and assess the ionizing radiation dose received by the human body due to external irradiation. The radiation dose may be determined during treatment planning for planning purpose, and/or during actual treatment for verification of delivery of dose.
Existing radiotherapy systems use electrons to generate the radiation beam. In such systems, the ability to control the dose placement is limited by the physics of the beam, which necessarily irradiates healthy tissue on the near-side and far-side of a target region as it passes through the patient. For particle therapy, beams of high energy charged particles, for example, protons but also heavier ions such as ionized carbon, oxygen and argon, may be used to deliver a therapeutic dose. Particle therapy offers improvements over more conventional electron and X-ray therapies by being able to deliver a dose much more precisely to a region within the body and with reduced unwanted damage to healthy tissues surrounding the region.
Proton therapy is a form of radiation therapy that uses protons to destroy targeted cells. Proton therapy can be an efficacious way to selectively destroy targeted cells because protons have unique dosimetric characteristics compared to other radiation, such as electrons or photons. Protons deposit most of their energy near the end of their path through a tissue. Because the dose provided by a proton is concentrated at a “Bragg peak” around the area where the proton stops, the dose to healthy tissue on the near-side of the target region may also be reduced. In this way, tissue on the far-side of the target region does not receive any radiation dose.
In contrast, photons deposit an exponentially decreasing amount of energy as a function of penetration depth. Thus, a proton therapy system can achieve greater targeted treatment compared to photon-based therapy (e.g., exposing targeted tissue to more radiation and/or healthy tissue to less radiation) because an operator can control a depth of penetration and dose profile of protons by selecting an initial energy of the protons. Proton irradiation requires beams to be directed to particular positions with good accuracy and with repeatable and timely control.
For particle therapy, accurate scanning and positioning of high energy particle beams is required. Until recently, proton therapy has been delivered using passive scattering. In this approach, the proton beam is expanded to subtend the entire tumor and the energy of the protons—and hence their stopping point in the tissue—is spread in range, to roughly match the tumor depth. Precise shaping of the exposure volume is provided by a specially constructed range correction compensator which provides additional range shifting to conform the distal edge of the beam to the distal edge of the tumor. This treatment approach essentially treats the entire tumor at once and, thus, is fast and yet less precise and requires the construction of a special compensator.
Lately, a more precise method called pencil beam scanning has been embraced. It offers a method of particle beam therapy for precise control and the ability to deliver a dose to the most complex volumetric shapes. In this approach, the proton beam remains narrowly collimated in a “pencil beam” and is steered in angle (deflection) and adjusted in range (energy) to deposit the dose as a small spot within the patient. For pencil beam scanning, angular deflection is typically less than ten degrees.
The spot is moved through the tumor in successive exposures until an arbitrary tumor volume has been irradiated. In combination with modulation of the beam intensity and sequential delivery of patterns at different beam energies, a desired dose distribution may be achieved. Several such exposures may be performed over a period of days or weeks in order to complete a treatment plan. This approach is potentially very accurate, but because the tumor is treated in successive exposures, is slower than the first approach. Further the small spot sizes create the risk of uneven dose placement or “cold spots” should there be patient movement between exposures.
For the foregoing reasons, it would be desirable to have systems and methods for accurately determining radiation dose and beam position while pencil beam scanning. It would also be desirable to have systems and methods for determining collimated beam profiles in two dimensions. The present disclosure contemplates the novel fabrication of a robust apparatus that provides for constant gain (or gain linearity), spatial resolution, minimal scattering of the ion beam and real time computation of peak position, width and accumulated dose, in addition to practical methods for manufacturing thereof and remedying these and/or other associated problems.